Following are acronyms used in the below description:                BPSK binary phase shift keying        CDMA code division multiple access        CPM continuous phase modulation        DFT discrete Fourier transforms        E-UTRAN evolved UTRAN        GSM global system for mobile communications        IDFT inverse discrete Fourier transform        OFDM orthogonal frequency division multiplexing        OFDMA orthogonal frequency division multiple access        SC-FDMA single-carrier frequency division multiple access        UTRAN universal mobile telecommunications system terrestrial radio access network        WiMAX worldwide interoperability for microwave access        
Cognitive radios use the radio spectrum in an opportunistic manner by avoiding interfering with primary users such as those operating normally using a GSM, UTRAN, or other more formalized communications protocol. Typically such formalized protocols entail radio resources being assigned by a centralized entity such as a base station, but cognitive radios are assumed to also avoid interfering with radios operating in systems that use contention-based radio access, such as Bluetooth for example. Development of cognitive radio systems is at an early stage, and some cognitive radio systems under development may have a specific spectrum band allocated and may even have some central node, but in all instances the individual cognitive radios operate using the spectrum opportunistically. There are various proposals for cognitive radio operations, many of which assume that the cognitive radio transmissions will be OFDM based.
More generally, cognitive radio may be considered to be a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently. The objective is to avoid interference with licensed (e.g., GSM, UTRAN, E-UTRAN CDMA) or unlicensed (e.g., Bluetooth) radio spectrum users. The alteration of transmission parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and the network state.
One of the earliest introductions to cognitive radio is an article by Joseph Mitola III and Gerald Q. Maguire, Jr [Cognitive Radio: Making Software Radios More Personal, IEEE PERSONAL COMMUNICATIONS MAGAZINE, August 1999, pp. 13-18]. Since then there has been a significant research effort within the academic and industrial communities to develop cognitive radio/spectrum sharing techniques that can be applied to future communications networks. Shared spectrum usage is an evolving topic that falls under the broad canopy of cognitive radio. Cognitive radio is an emerging topic which many companies and universities are investigating with a projected timeline of 10-12 years for actual system deployment. These teachings hope to advance that timeline as follows.
A problem is anticipated in that different radios, designed to operate according to different radio standards, may prefer to engage in cognitive radio communications with one another. If one regimen for cognitive radio procedures becomes largely accepted, how will other radios designed for protocols that are not consistent with that accepted procedure operate in the cognitive spectrum sharing mode? Cooperative, interference-free spectrum sharing between radios that are normally designed to operate using different standards (e.g., WiMAX, which is OFDM-based; GSM, which is CPM-based; and CDMA 1x) is seen to be an important aspect to avoid resistance by those with a vested interest in the different standards to agreeing to one specific regimen for cognitive radio. This ability to inter-operate among different radios designed for different systems/protocols is seen as likely to advance the cognitive radio concept more quickly toward widescale implementation.
For example, WiMAX and LTE radios use OFDM while GSM and Bluetooth radios use variants of continuous phase modulation CPM, and CDMA (1x) radios use code division multiple access (CDMA). Their physical layer formats are not compatible with one another and, if allowed to operate over the same band without any modifications, will harmfully interfere with each other. As shown in FIG. 1, when the working bands of different non-cooperative systems overlap as is seen between the CDMA receiver and the GSM transmitter, then the result is co-channel and adjacent channel interference. Co-channel interference may be handled by moving the carriers of the two systems farther apart in order to minimize the portion of the spectrum over which they overlap. However, this solution reduces the spectral efficiency of both systems since portions of the radio spectrum go unused. Adjacent channel interference is typically suppressed by dedicated receiver filtering operations, which can be designed to minimize their impact to bit error rate performance.
The inventor is aware of no other algorithm or invention which facilitates spectrum usage between radios that normally operate over different air interfaces without requiring significant hardware/software changes to the radios. These teachings are directed to facilitating such spectrum sharing, in a manner that does not require significant hardware changes to the devices that communicate using the cooperatively shared spectrum. It will be appreciated from the description below that the invention is not limited to the cognitive environment, and can be used by a radio whose transmissions are sent in an E-UTRAN system for example.